Effect of alkaline treatment and weathering on the mechanical properties, failure mechanisms and service life of jute, hemp, and sisal fiber-reinforced epoxy biocomposites

This study investigates the influence of alkaline treatment and accelerated weathering on the mechanical behaviour, failure mechanisms, and service life of natural fiber-reinforced epoxy biocomposites. Jute, hemp, and sisal fibers were chemically modified using sodium hydroxide (NaOH: 1%, 5%, 10%) and sodium bicarbonate (NaHCO₃: 5%, 10%, 15%) to enhance interfacial bonding and reduce moisture uptake. Composite laminates were prepared using the hand lay-up technique and tested for tensile, flexural, and interlaminar shear strength (ILSS) under both unweathered and weathered conditions involving UV exposure, elevated temperature, and high humidity. Fractographic analysis was conducted to observe failure characteristics, while water absorption tests and service life predictions were used to assess moisture resistance and long-term stability. Among all formulations, 5% NaOH-treated hemp composites exhibited the best mechanical performance, achieving tensile, flexural, and ILSS values of 58.86 MPa, 80.16 MPa, and 9.15 MPa, respectively. Water absorption tests confirmed hemp’s superior resistance to moisture, followed by sisal and jute, which aligned with strength retention trends after weathering. After 1008 hours of environmental exposure, 5% NaOH-treated hemp composites retained 77.25% of their tensile strength, 77.7% of flexural strength, and 71.3% of ILSS. Fractographic observations revealed strong fiber-matrix adhesion in treated composites, with reduced fiber pull-out, whereas untreated samples showed significant fiber debonding and, in some cases, complete sample failure under weathering. Service life estimation, based on 50% strength retention, projected up to 2.17, 2.26, and 1.73 years of effective use for tensile, flexural, and ILSS properties, respectively. Future research can investigate hybrid fiber configurations and alternative resin systems to improve durability • 5% NaOH-treated composites exhibited the highest mechanical properties across all biocomposites. • Fractographic analysis revealed improved fiber–matrix adhesion and reduced fiber pull-out in treated samples. • Hemp fiber composites demonstrated the greatest moisture resistance in water absorption tests. • Service life prediction estimated up to 2.17, 2.26 & 1.73 years of durability for hemp composites under accelerated weathering.